Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible, but not significantly extensible.
In many cases, ligaments are torn or ruptured as a result of trauma. As a result, various procedures have been developed to repair or replace such damaged ligaments.
For example, in the human knee, the anterior and posterior cruciate ligaments extend between the top end of the tibia and the bottom end of the femur. The anterior and posterior cruciate ligaments cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the anterior cruciate ligament (hereafter, the “ACL”) is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee.
In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a graft ligament. More particularly, with such procedures, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways known in the art so that the graft ligament extends between the femur and the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore normal function to the knee.
In some circumstances, the graft ligament may be a ligament or tendon which is harvested from elsewhere in the patient (autograft) or from a cadaveric donor (allograft) (e.g., a hamstring); in other circumstances, the graft ligament may be a synthetic device. For the purposes of the following description, all of these types of ACL-replacing tissues will be collectively referred to as a “graft ligament”.
The native ACL is not simply a band of connective tissue, but has a complex and partially twisted “double-bundle” structure in which an anteromedial portion/bundle of the ACL controls the forward-backward pivoting of the joint, and a posterolateral portion/bundle of the ACL controls rotational stability of the joint. When the knee is straight, these two bundles extend in a parallel manner between the femur and tibia. When the knee is flexed, the two bundles cross each other. The anteromedial and posterolateral bundles are subtly different in the manner in which they mechanically interact with each other and with other components of a healthy knee joint. For example, the anteromedial and posterolateral bundles may be under different amounts and/or directions of tensile force within the knee joint. It is common for patients with ACL injuries to have damage to both the anteromedial and posterolateral bundles.
Traditionally, a single graft ligament has been used to restore knee function to the patient by merely approximating the function of the native ACL. A single-graft technique involves drilling a single bone tunnel in each of the femur and tibia. This technique is well-established in the art and is considered a routine surgical procedure, after which patients typically return to their normal level of activity. However, a single-graft reconstruction does not reflect the original knee structure and therefore might lead to future adverse effects due to long-term use of the knee in a mechanically different configuration than the native anatomy.
In the last several years, surgeons have begun to refine their techniques to better mimic the double-bundle structure of the native ACL, as well, in the interest of creating a more “natural” replacement ACL and with the goal of a better long-term prognosis for achieving normal function of the reconstructed knee joint. One currently used double-bundle ACL replacement technique requires separate bone tunnels to be provided for each of the two reconstructive grafts. However, drilling two tunnels in close proximity is technically difficult and brings about a heightened risk of complication.
In a variation on this known technique, the two graft ligaments replacing the anteromedial and posterolateral bundles of the ACL both run from a single femoral bone tunnel to a single tibial bone tunnel. Due to the limited confines of the bone tunnels, traditional graft-anchoring techniques may not be effective in placing dual graft ligaments within a single tunnel. An example of a commercially available system which has been developed to address the specialized anchoring needs of a double-bundle ACL replacement is the AperFix™ system, available from Cayenne Medical of Scottsdale, Ariz. However, the AperFix™ product is limited in the manner in which each of the two graft ligaments can be manipulated (requiring a substantially symmetrical and simultaneous placement, tensioning, and anchoring of these two graft ligaments) and in aligning the bundles to replicate the placement of a native ACL within a single tunnel. Therefore, the graft ligaments used with currently available double- or single-tunnel systems do not, and cannot, accurately approximate the complex and individually varying mechanical interactions of the anteromedial and posterolateral bundles of a native ACL.